In recent years, liquid crystal display devices are often used as flat panel displays in various fields. Contrast and tinge greatly vary depending, on viewing angles. A need for a light source such as a backlight hinders reduction in power consumption. Reduction in the thickness and weight of a liquid crystal device is limited. These serious problems still remain. Liquid crystal devices have also serious problems in flexibility.
To address the problems, self-luminous organic EL display devices using an organic EL element are expected in place of liquid crystal display devices in recent years. In an organic EL element, a current flows through an organic EL layer between an anode and a cathode so that organic molecules forming the organic EL layer emit light. Being self-luminous, organic EL display devices using such an organic EL element are excellent in reducing the thickness, weight, and power consumption. In addition, organic EL display devices provide a wide viewing angle, and thus draw great attentions as flat panel display candidates in next generation.
Organic EL display devices using a plastic substrate draw special attentions. A plastic substrate has higher flexibility, higher shock resistance, and lower weight than a glass substrate. A plastic substrate would provide new organic EL display devices beyond typical display devices using a glass substrate.
However, in general, after a certain period of drive, light-emitting characteristics, such as brightness and uniformity in light emission, of an organic EL element deteriorate significantly from the initial state. The deterioration in the light-emitting characteristics attributes to deterioration of an organic layer due to moisture of outside air, which has entered the organic EL element, or removal of the organic layer from an electrode due to moisture.
To address the problems, providing a sealing film to reduce entry of gas generated by moisture is disclosed. Specifically, a disclosed functional film includes a flexible plastic substrate (e.g., a film substrate), and an inorganic film (e.g., a SiOX thin film) on the plastic substrate. The inorganic film is deposited on the plastic substrate at a rate of 3 to 10 Å/sec, and compressive residual strain of 0.4 to 0.6% (stress of 280 Mpa to 430 Mpa) is applied to the inorganic film to be formed. This method increases compressive residual stress of an inorganic film, thereby manufacturing the inorganic film with increased fracture strain (see, e.g., Patent Document 1).